1. Field of the Invention
The present invention relates to a propylene glycol cyclohexyl ether derivative. More particularly, the present invention is concerned with a novel propylene glycol cyclohexyl ether derivative having a cyclohexyl or monohydroxycyclohexyl group at a specific position in the molecule, and a method for producing the same. The propylene glycol cyclohexyl ether derivative of the present invention is not only extremely safe by virtue of its low toxicity and high flash point, but also has excellent detergency, low viscosity, and can impart a high film-forming ability to a resin emulsion. Further, this propylene glycol cyclohexyl ether derivative also has high hydrophobicity (and hence low water-solubility), so that it can minimize the cost and labor for disposal of waste water. Therefore, this propylene glycol cyclohexyl ether derivative is useful in various applications, for example, as a detergent, as a solvent for a wide variety of applications and as a film-forming agent. The present invention is also concerned with a detergent comprising this novel propylene glycol cyclohexyl ether derivative, which is particularly effective for removing ink used in screen printing, processing oils used in the processing of precision machinery parts and optical machinery parts, the flux used to solder electrical and electronic parts, and uncured epoxy adhesives. Furthermore, the present invention is concerned with an aqueous dispersion composition containing this novel propylene glycol cyclohexyl ether derivative, which is particularly useful as an aqueous paint.
2. Discussion of Related Art
In recent years, the prevention of environmental pollution and the improvement of work environment have been attracting great attention. Accordingly, it has become an urgent task to substitute solvents which cause environmental pollution or are toxic with solvents which do not cause these serious problems while exhibiting excellent performance.
For example, halogenated solvents, such as 1,1, 2-trichloro-1,2,2-trifluoroethane and 1,1,1-trichloroethane have low toxicity, nonflammability and excellent solvent properties and have therefore been widely used to remove processing oils used in the processing of precision machinery parts and optical machinery parts and the flux used to solder electrical and electronic parts. The use of such halogenated solvents, however, has also been found to cause serious problems, such as the destruction of the protective ozone layer surrounding the earth contributing to global warming, so that their use will be prohibited in the future.
As substitutes for the above-mentioned halogenated solvents, various solvents have been proposed. However, such substitute solvents also have posed various problems. For example, terpenes, which are non-halogenated solvents, exhibit excellent detergency, but have a disadvantageously low flash point, so that safety during use cannot be ensured.
Further, glycol monoalkyl ether derivatives have been proposed as substitute solvents (see, for example, Unexamined Japanese Patent Application Laid-Open Specification Nos. 3-162496 and 3-97792), but these conventional glycol monoalkyl ether derivatives also have problems. When the number of carbon atoms of the alkyl groups of these compounds is relatively small (as in diethylene glycol monobutyl ether), the solubility of the compounds in water is disadvantageously high, so that the waste water is likely to be contaminated with the compound, leading to difficulties in disposing the waste water. On the other hand, when the number of carbon atoms of the alkyl groups is relatively large (as in diethylene glycol monohexyl ether), the solubility of the compounds in water is low and the contamination of the waste water with the compounds can be avoided, but the compounds have disadvantageously high viscosity and thus poor detergency.
Glycol dialkyl ether derivatives have also been proposed as substitute solvents (see, for example, Unexamined Japanese Patent Application Laid-Open Specification No. 3-227400), but these compounds have drawbacks in that, for example, diethylene glycol dimethyl ether and diethylene glycol diethyl ether, which are described in the working Examples of the above Application, not only exhibit high toxicity, but also have extremely high solubility in water, so that waste water is likely to be contaminated with such compounds, leading to an increase in the cost for the disposal of the waste water.
Thus, satisfactory glycol ether type solvents, which can be safely used, for example, as detergents and paint compositions, have heretofore not been known.
Ethylene glycol solvents which were widely used in paint and ink compositions have been substituted with less toxic propylene glycol solvents, particularly propylene glycol ether derivatives, which are obtained by etherifying propylene glycol with lower alkyl groups, such as methyl, ethyl, and butyl. However, these propylene glycol ether derivatives have high solubility in water, so that the use of such derivatives causes the waste water to be contaminated therewith, leading to difficulties in disposing the waste water. Particularly, in the field of paints, there is a trend toward switching from non-aqueous paints to aqueous paints in order to reduce the amount of non-aqueous solvents used. This trend of using water as a part of the solvent has increased the above-mentioned difficulties in disposal of the waste water when water is used in combination with the propylene glycol ether derivatives.
Further, in aqueous paints, the use of film-forming agents which serve to facilitate the formation of a paint film (and which are not needed when non-aqueous solvents are employed) is needed. Examples of conventional film forming agents include, N-methylpyrrolidone (NMP), 2,2,4-trimethyl-1,3-pentanediol isobutyrate, butyl cellosolve, polypropylene glycol derivatives and the like. Such film-forming agents, however, have the problems of high hydrophilicity, unpleasant odor, toxicity and the like.
Accordingly, it has been earnestly desired to develop a novel compound having properties, such as low toxicity, excellent safety (i.e., nonflammability and a high flash point), high hydrophobicity, high detergency, high solvency, high capability to facilitate film formation, and the like, so that it can be advantageously used as a solvent, a detergent or a film-forming agent.
In order to satisfy the above-mentioned requirements, several techniques have been proposed.
For example, Unexamined Japanese Patent Application Laid-Open Specification No. 3-62895 discloses an ethylene glycol ether derivative and a propylene glycol ether derivative which have a higher alkyl group, such as an n-hexyl group. These glycol ether derivatives, however, are very poor in detergency, although their solubility in water is relatively low. When the chain lengths of the alkyl groups of such glycol ether derivatives are increased, hydrophobicity is improved, but the boiling point and viscosity become disadvantageously high. Thus, these glycol ether derivatives are not suitable for practical use.
Further, Unexamined Japanese Patent Application Laid-Open Specification Nos. 4-57897 and 4-57898 disclose the reaction of a propylene oxide with cyclohexanol. By this reaction, propylene glycol monocyclohexyl ether represented by the formula shown below is produced with a selectivity of about 100%. ##STR2## This compound, however, not only has high solubility in water, leading to difficulties in disposing waste water containing this compound, but is also disadvantageous in that it has high viscosity, poor dissolving power for oils, and low drying rate. Accordingly, this compound is not useful in practice.
Thus, there are no compounds in the art which simultaneously satisfy all of the requirements mentioned above for use as solvents, detergents and film-forming agents.